Recently, according to the prediction of existing energy resources such as petroleum, coal and the like being exhausted, alternative energy resources have attracted considerable attention. Among these alternative energy resources, solar cells for directly converting solar energy into electrical energy using a semiconductor device are spotlighted as a next-generation cell. Solar cells are largely classified into silicon solar cells, compound semiconductor solar cells and tandem solar cells. Among such solar cells, silicon solar cells are generally used.
Meanwhile, in order to manufacture a high-efficiency solar cell, various components, such as a shallow emitter, a selective emitter and the like, have been developed. The shallow emitter, which is called an emitter layer having a high surface resistance of 60˜120 Ω/sq, is applied to a high-efficiency solar cell because it has a low recombination rate and can use short-wavelength solar light.
The emitter layer of a general solar cell has a thickness of 600 nm or more, whereas the emitter layer of a high-efficiency solar cell has a thickness of 100 to 500 nm, which is an ultra-slim emitter layer. Therefore, the emitter of a high-efficiency solar cell is problematic in that, at the time of forming an electrode, an electrode comes into contact with a base through a thin emitter layer, and thus the electrode easily short-circuits. That is, in order to commercially use a high-efficiency solar cell including a thin emitter layer, a process for easily bringing an electrode into contact with a thin emitter layer and preventing the electrode from coming into contact with a silicon substrate (base) and short-circuiting is required.
As a method of using the advantage of a shallow emitter and solving the disadvantage thereof, Korean Patent Application No. 2010-7022607 discloses a method of forming a nickel (Ni)-silicide layer by heat-treating a nickel (Ni) layer having low contact resistance. Here, the method for forming a nickel (Ni)-silicide layer further includes the steps of selective electroless plating and then annealing a nickel layer to form a nickel-silicide layer, electroplating the nickel-silicide layer to form a plurality of contact sites thereon, and forming a low-resistance contact line for a photovoltaic device. However, this method is problematic in that it is complicated because it needs an electroless plating process and a selective plating process in order to form a nickel layer, and in that costs increase.
Therefore, it is required to develop a simple process for forming a nickel layer having low contact resistance.